diff --git a/gnu/machine/hetzner.scm b/gnu/machine/hetzner.scm
index fdc22b4c05..c19f0ebc81 100644
--- a/gnu/machine/hetzner.scm
+++ b/gnu/machine/hetzner.scm
@@ -152,7 +152,7 @@
       (operating-system
         (inherit os)
         (services
-         (modify-services (operating-system-user-services os)
+         (modify-services services
            (guix-service-type
             config => (guix-configuration
                        (inherit config)
diff --git a/gnu/services/virtualization.scm b/gnu/services/virtualization.scm
index 3c9aadaae3..7d15abaf61 100644
--- a/gnu/services/virtualization.scm
+++ b/gnu/services/virtualization.scm
@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2017 Ryan Moe <ryan.moe@gmail.com>
-;;; Copyright © 2018, 2020-2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2020-2026 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2020, 2021, 2023, 2024 Janneke Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2021 Timotej Lazar <timotej.lazar@araneo.si>
 ;;; Copyright © 2022, 2025 Oleg Pykhalov <go.wigust@gmail.com>
@@ -1211,7 +1211,7 @@ that will be listening to receive secret keys on ADDRESS."
      ;; those keys are going to be overwritten by secrets received from the
      ;; host anyway.
      (cons (service secret-service-type address)
-           (modify-services (operating-system-user-services os)
+           (modify-services services
              (openssh-service-type
               config => (openssh-configuration
                          (inherit config)
diff --git a/gnu/system/vm.scm b/gnu/system/vm.scm
index a3db2991d6..626b5039ac 100644
--- a/gnu/system/vm.scm
+++ b/gnu/system/vm.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013-2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013-2026 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 Christine Lemmer-Webber <cwebber@dustycloud.org>
 ;;; Copyright © 2016, 2017 Leo Famulari <leo@famulari.name>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
@@ -185,7 +185,7 @@ environment with the store shared with the host.  MAPPINGS is a list of
     ;; XXX In 6.14, the kernel renamed the "cirrus" module to "cirrus-qemu", so
     ;; we account for that here. The renaming was done in this commit:
     ;; https://git.kernel.org/pub/scm/linux/kernel/git/sashal/linux-stable.git/commit/?id=5c3c99868aa2e0b68ac69f8050a6b9c994e73397
-    (initrd-modules (let* ((modules (operating-system-initrd-modules os))
+    (initrd-modules (let* ((modules initrd-modules)
                            (kernel-version
                              (package-version (operating-system-kernel os)))
                            (cirrus-module
diff --git a/gnu/tests.scm b/gnu/tests.scm
index abb7076208..aa0875ba5c 100644
--- a/gnu/tests.scm
+++ b/gnu/tests.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016-2020, 2022-2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016-2020, 2022-2026 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
@@ -274,7 +274,7 @@ the system under test."
   (operating-system
     (inherit os)
     (services
-     (modify-services (operating-system-user-services os)
+     (modify-services services
        (shepherd-system-log-service-type
         config
         =>
diff --git a/gnu/tests/avahi.scm b/gnu/tests/avahi.scm
index d7f2fdaa72..21d8995a6d 100644
--- a/gnu/tests/avahi.scm
+++ b/gnu/tests/avahi.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016-2020, 2022, 2024-2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016-2020, 2022, 2024-2026 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -46,8 +46,7 @@
                      (service dhcpcd-service-type) ;needed for multicast
 
                      ;; Enable heavyweight debugging output.
-                     (modify-services (operating-system-user-services
-                                       %simple-os)
+                     (modify-services services
                        (nscd-service-type config
                                           => (nscd-configuration
                                               (inherit config)
diff --git a/gnu/tests/base.scm b/gnu/tests/base.scm
index b65e54222c..92bf4b4a11 100644
--- a/gnu/tests/base.scm
+++ b/gnu/tests/base.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016-2020, 2022, 2024-2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016-2020, 2022, 2024-2026 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Clément Lassieur <clement@lassieur.org>
 ;;; Copyright © 2022, 2025 Maxim Cournoyer <maxim@guixotic.coop>
 ;;; Copyright © 2022 Marius Bakke <marius@gnu.org>
@@ -1348,7 +1348,7 @@ runs unprivileged.")
                                  (group "users"))
                                 %base-user-accounts))
                    (services
-                    (modify-services (operating-system-user-services base)
+                    (modify-services services
                       (guix-service-type
                        config => (guix-configuration
                                   (inherit config)
diff --git a/gnu/tests/nfs.scm b/gnu/tests/nfs.scm
index 0453d45382..e760c4502a 100644
--- a/gnu/tests/nfs.scm
+++ b/gnu/tests/nfs.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016-2017, 2020-2021, 2025 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016-2017, 2020-2021, 2025-2026 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 John Darrington <jmd@gnu.org>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
@@ -170,7 +170,7 @@
                      %base-file-systems))
       (services
        ;; Enable debugging output.
-       (modify-services (operating-system-user-services os)
+       (modify-services services
          (shepherd-system-log-service-type
           config
           =>
@@ -285,7 +285,7 @@ directories can be mounted.")
                      (exports '(("/export"
                                  "*(rw,insecure,no_subtree_check,\
 crossmnt,fsid=root,no_root_squash,insecure,async)")))))
-           (modify-services (operating-system-user-services os)
+           (modify-services services
              (shepherd-system-log-service-type
               config
               =>